Temporal changes in the structure and diversity of the floral fungal community of Leptospermum scoparium (mānuka)

Abstract

Flowers of the New Zealand indigenous tree, Leptospermum scoparium (mānuka), play a key role in the commercial value of the antimicrobial mānuka honeys. As an ephemeral but complex and nutrient-rich structure, the flower provides a specialized habitat for microbial communities (anthosphere)¹. The increasing awareness of the role of microbial communities in plant health², and the importance of flowers in agricultural and natural ecosystems, calls for a greater understanding of the anthosphere structure and dynamics. The goal of the study was to characterize for the first time, the fungal community structure and assembly dynamics of the anthosphere throughout the flower life cycle. To accomplish this, six floral stages; immature bud, bud, bud burst, mature f lower, spent flower and seed, were sampled from five individuals mānuka trees from the same environment. A total of 203 anthosphere samples and 35 phyllosphere samples were analysed using metabarcoding approaches targeting the ITS1 region. The results shown that the different microbial reservoirs leaf, mature flower, and seed shared many members but had distinct fungal communities. Mānuka anthosphere was dominated by yeasts from Aureobasidium, Vishniacozyma genera and filamentous fungi from Cladosporium genus. A core group of fungal taxa was identified to occur throughout the flower life cycle and represented between 23 to 63% of the total taxa at each floral stage. Temporal patterns in fungal richness was observed, with an increase in richness from immature bud to mature flower and decrease from spent flower to seed. Fungal community assembly was more impacted by arriving taxa in the first stages, whereas taxa common with the previous stage was more predominant from mature flower to seed. Finally, floral stages closer in time had similar fungal community, whereas stages separate by at least one stage showed more distinct fungal communities. This study demonstrated that floral stages are a strong driver of mānuka anthosphere fungal community assembly and dynamics. These results enhance our understanding of the floral microbial communities assembly sources and ecological interactions.